Mystic Decree 
World Enchantment
$0.97 #25317 0.32 31.1 years
All creatures lose flying and islandwalk.
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Cards similar to Mystic Decree expected a card that isn't here?
Reports become test cases the matcher is graded against before an update ships. Delvefall isn't a chatbot guessing, it compares the printed rules text of every card with plain math, and examples like yours decide which differences should count.
Gravity Sphere85%
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"All creatures lose flying."
Whiteout72%
$0.28↓#251550.3331.4 years
"All creatures lose flying until end of turn."
Undertow72%
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"Creatures with islandwalk can be blocked as though they didn't have islandwalk."
Gosta Dirk72%
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"Creatures with islandwalk can be blocked as though they didn't have islandwalk."
Lord Magnus71%
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"Creatures with forestwalk can be blocked as though they didn't have forestwalk."
Ur-Drago70%
$18.27↑#31204↓0.00↓32.4 years↑
"Creatures with swampwalk can be blocked as though they didn't have swampwalk."